The exhaust purification catalyst for a vehicle engine can not fully perform at a low temperature.
In order to cope with this situation, Tokkai Hei 7-167284 published by Japanese Patent Office in 1995 discloses a method to prevent an automatic transmission from using a highest gear e.g., overdrive gear, when the temperature of the exhaust purification catalyst is low. This arrangement results in the increase the engine rotation speed that promotes the activation of the catalyst.